Fix incorrect GTK menus on HiDPI monitors with scaling factor > 1

This should fix Bug#31223, Bug#28106, Bug#23672 as well as Ubuntu bug
https://bugs.launchpad.net/ubuntu/+source/emacs25/+bug/1695228

Also fixes the formerly unscaled Y value returned by
frame-monitor-workarea (and display-monitor-attributes-list).

For details on why some GTK menus were empty please see thread
https://lists.gnu.org/archive/html/emacs-devel/2019-11/msg01061.html

* src/gtkutil.c (menubar_map_cb, xg_update_frame_menubar): Scale up
req.height so that the menu bar's height is in device pixels as
expected.
(xg_event_is_for_menubar): Scale down rec.x and rec.y so that
gtk_widget_intersect() works as intended.
* src/xfns.c (Fx_display_monitor_attributes_list): Scale work.x and
work.y up to be in device pixels.

Copyright-paperwork-exempt: yes

2 files changed, 7 insertions, 3 deletions

diff --git a/src/gtkutil.c b/src/gtkutil.c
index cf5c31aa203..7e6db57c9dd 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -3471,6 +3471,7 @@ menubar_map_cb (GtkWidget *w, gpointer user_data)
   GtkRequisition req;
   struct frame *f = user_data;
   gtk_widget_get_preferred_size (w, NULL, &req);
+  req.height *= xg_get_scale (f);
   if (FRAME_MENUBAR_HEIGHT (f) != req.height)
     {
       FRAME_MENUBAR_HEIGHT (f) = req.height;
@@ -3502,7 +3503,7 @@ xg_update_frame_menubar (struct frame *f)
   g_signal_connect (x->menubar_widget, "map", G_CALLBACK (menubar_map_cb), f);
   gtk_widget_show_all (x->menubar_widget);
   gtk_widget_get_preferred_size (x->menubar_widget, NULL, &req);
-
+  req.height *= xg_get_scale (f);
   if (FRAME_MENUBAR_HEIGHT (f) != req.height)
     {
       FRAME_MENUBAR_HEIGHT (f) = req.height;
@@ -3568,8 +3569,9 @@ xg_event_is_for_menubar (struct frame *f, const XEvent *event)
 
   list = gtk_container_get_children (GTK_CONTAINER (x->menubar_widget));
   if (! list) return 0;
-  rec.x = event->xbutton.x;
-  rec.y = event->xbutton.y;
+  int scale = xg_get_scale (f);
+  rec.x = event->xbutton.x / scale;
+  rec.y = event->xbutton.y / scale;
   rec.width = 1;
   rec.height = 1;
 
diff --git a/src/xfns.c b/src/xfns.c
index b1b40702c24..47aa19607f6 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -5093,6 +5093,8 @@ Internal use only, use `display-monitor-attributes-list' instead.  */)
 #endif
       rec.width *= scale;
       rec.height *= scale;
+      work.x *= scale;
+      work.y *= scale;
       work.width *= scale;
       work.height *= scale;